This invention relates to a wireline tractor. More particularly, it relates to a wireline tractor comprising at least one driving wheel positioned on a displacement mechanism connected to the wireline tractor, in which the displacement mechanism is arranged so as to hold the driving wheel in a biasing manner against a well wall. The displacement mechanism is at least rotatable or movable between a first position at which the driving wheel bears against the well wall on one side of the wireline tractor, and a second position at which the driving wheel bears against the well wall on the opposite side of the wireline tractor.
In this connection, wireline tractor implies a unit which, when provided with supplied or stored energy, is arranged so as to be able to move itself within an open or cased borehole.
Wireline tractors have assumed considerable application in, for example, outfitting and maintenance work in petroleum wells. Many wireline tractors are provided with driving wheels which are biased against the well wall, the driving wheels moving the wireline tractor down into the well. A connected cable or pipe is oftentimes used to pull out the wireline tractor from the well.
Each driving wheel may be positioned on a swivel arm rotatably connected to the wireline tractor, in which the swivel arm is provided with required driving elements for transmitting motive power from the wireline tractor and onto the respective driving wheel. By virtue of the driving wheel being connected to a free end portion of its respective swivel arm, the driving wheel is arranged so as to be able to accommodate relatively large variations in well diameter.
During some work operations it would prove advantageous if possible to change the direction of rotation of the driving wheels so as to be able to move the wireline tractor in the opposite direction.
Due to limited space, among other things, it has proven difficult to provide wireline tractors with reversible driving wheels.